This invention relates generally to gas turbine engines, and more particularly, to methods and apparatus for operating gas turbine engines.
Gas turbine engines typically include high and low pressure compressors, a combustor, and at least one turbine. The compressors compress air which is mixed with fuel and channeled to the combustor. The mixture is then ignited for generating hot combustion gases, and the combustion gases are channeled to the turbine which extracts energy from the combustion gases for powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Because gas turbine engines must be capable of operating in a plurality of operating conditions, the engines include control systems to control engine operations. More specifically, the control systems compare inputs received from engine parameters, such as rotational speed of a fan, to power management schedules preloaded in the control systems.
When engines operate in icing conditions, ice may accumulate on the low pressure compression system of the engine. More specifically, if such engines are operated within icing conditions at low power for extended periods of time, ice accumulation within the engine may be significant. Over time, continued operation of the engine, or a throttle burst from lower power operations to higher power operations, may cause the accumulated ice build-up to separate from the low pressure compression system and be ingested by the high pressure compressor. Such a condition is known as an ice shed, and may cause compressor discharge temperature to be suddenly be reduced. In response to the sudden decrease in compressor discharge temperature, the corrected core speed increases in the aft stages of the high pressure compressor. This sudden increase in aft stage corrected core speed may adversely impact compressor stall margin.
In an exemplary embodiment, a fuel control system for a gas turbine engine includes logic used to facilitate enhanced compressor stall margin when the engine is operating in potential icing conditions. The fuel control system is coupled to at least one fuel regulator within the engine, and receives input from a plurality of sensors coupled to the engine. More specifically, the system receives input from environmental sensors, as well as inputs representing compressor inlet temperature, compressor discharge pressure, and corrected core engine speed. In addition, the fuel control system also receives input from other engine fuel regulators.
During operation, the fuel control system determines a maximum fuel flow deviation in response to inputs received from the engine and environmental sensors. The maximum fuel flow deviation is scaled in response to inputs received from the environmental sensors, and is used to determine fuel regulator priority selection and a commanded fuel flow. The commanded fuel flow is adjusted to be maintained within pre-defined maximum and minimum fuel flow demand limits. As a result, the fuel control system facilitates enhanced compressor stall margin when the engine is operating in potential icing conditions, and thus eliminates compressor stall margin shortfalls that may occur following a compressor ice shed event.